Another family member of a victim was frustrated the legal proceedings had taken so long.

"My understanding is that British police possessed all the evidence that resulted in the decision announced today in the US," Donald Main, whose niece, Ruth Williamson, was killed.

"I have never understood why this judgement could not have been made many years ago by a UK court, thus avoiding the long very costly legal battles seeking to avoid extradition to the US."

In a statement, the Crown Prosecution Service said it had considered evidence related to the Yemen plot on "two separate occasions" but there said there was "simply insufficient evidence to allow a prosecution of those offences at the time".

Media playback is unsupported on your device

Media captionLaurence Whitehouse's wife, Margaret, was killed when they were both kidnapped.

Abu Hamza was also convicted of helping to set up a terrorist training camp in the US state of Oregon.

His trial followed his extradition to the US in 2012 at the end of an eight-year legal battle.

During his trial Abu Hamza was described as a "terrorist facilitator with a global reach".

He had used his powerbase at the Finsbury Park Mosque in north London to encourage his followers to train and fight in the cause of jihad.